Boron essential for alfalfa, but don't pour on more than needed

WEST LAFAYETTE, Ind. -
Alfalfa growers should consider whether or not boron should be added to their potassium and phosphorus application, said a Purdue University specialist.

Alfalfa requires more boron than other crops for good growth and productivity, said Keith Johnson, Purdue Extension forage management specialist.

"It's an essential micronutrient for all plants, but alfalfa requires higher amounts," Johnson said. "Boron is more likely to be deficient in soils with low organic matter, sandy soils and in the unglaciated soils of southern Indiana."

Symptoms of boron deficiency include a shortening of the plant's internodes, which leads to a shorter plant and yellowing, Johnson said.

"It actually looks very similar to potato leafhopper damage," he said.

Growers should randomly collect the upper 6 inches of 50 alfalfa plants and submit plant tissue to a laboratory for analysis. A tissue analysis costs between $20 and $30 and could more than pay for itself if there is a deficiency, he said. A list of laboratories is available online at http://www.agry.purdue.edu/ext/soiltest.html

"Because boron is a micronutrient, an application of only 1 to 3 pounds per acre per year is sufficient if the tissue test indicates a need," Johnson said. "It may be that boron only needs to be applied every other year. It's important to have a tissue analysis done because it can be beneficial from a cost savings standpoint, and too much can be toxic for a following corn, soybean or other grain crop."

Growers should check and make sure they get what they asked for from their fertilizer dealers, Johnson said.

"Some may get a standardized mix with potassium, phosphorus and boron when a grower may not need to add boron this year," he said. "It's best to check and make sure everything matches up from what the soil needs to produce a good stand, to what you're purchasing and applying."

Jim Camberato, Purdue Extension soil fertility specialist, said if a tissue analysis shows a need for boron, it can be foliar applied when it's not practical to apply the granular form.

"The foliar application of boron should be sprayed on alfalfa stubble after a cutting if possible and should be limited to no more than 0.5-pound of boron per acre to minimize foliage burn," Camberato said. "If a field is very low in boron, multiple foliar applications may be needed to fulfill the crop's boron requirement."

If boron is combined with a pesticide, growers should check both the fertilizer and pesticide labels to ensure compatibility, Camberato said.